I restored my iPhone but now it doesn't have a carrier?

I restored my iPhone yesterday and now in the top left corner it doesn't say sprint, Verizon, or AT&T. What do I do? It was originally from Verizon but I want it from sprint. Because I bought It from eBay and it was Verizon and I have sprint. Do I just take it to the sprint store and say " can I add this phone to my plan"? What do I do or say to sprint?

Why don't you just go to Simple Mobile & buy one of their sim cards. It's cheaper.

No because the sprint store will reject the unlock because it is a Verizon phone and Verizon won't unlock it because it will be used for a different carrier. Try finding a website that can do it for you. I was in the same situation as you for at&t to T-Mobile and I used unlockatt on Google. They unlocked my iPhone and helped me out for a decent price.